Certain disease states require treatment using one or more different medicaments. Some drug compounds need to be delivered in a specific relationship with each other in order to deliver the optimum therapeutic dose. Here, combination therapy may be desirable, but not possible in a single formulation for reasons such as, but not limited to, stability, compromised therapeutic performance and toxicology.
For example, in some cases it might be beneficial to treat a diabetic with a long acting insulin and with a glucagon-like peptide-1 (GLP-1), which is derived from the transcription product of the proglucagon gene. GLP-1 is found in the body and is secreted by the intestinal L cell as a gut hormone. GLP-1 possesses several physiological properties that make it (and its analogs) a subject of intensive investigation as a potential treatment of diabetes mellitus. Another example of a medicament combination is the administration of a pain reliever in combination with a medicament for treating osteoarthritis.
Drug delivery devices of the aforementioned kind often have applications where regular injection by persons without formal medical training occurs. This is increasingly common among patients having diabetes or the like, e.g. osteoarthritis. Self-treatment enables such patients to conduct effective management of their disease.
In combination therapy, a primary medicament and a secondary medicament are delivered in a specific relationship to deliver the optimum therapeutic dose. The injection devices of the generic kind usually comprise a housing or a housing assembly in which two or more drug delivery assemblies are retained. Such devices include a primary drug delivery assembly for dispensing the primary medicament such as the long-acting insulin and a secondary drug delivery assembly for dispensing the secondary medicament, such as GLP-1. Some kinds of drug delivery assemblies comprise a compartment such as a cartridge holder for accommodating a replaceable medicament container such as a cartridge which stores the medicament.
In some cases, depending on the patient or the stage of the therapy, an effective treatment requires variations in the quantities and/or proportions of the medicaments making up the combined therapy. For example, the patient may require a non-adjustable fixed dose of the secondary medicament in combination with an adjustable variable dose of the primary medicament. The primary medicament and the secondary medicament are each contained in a single cartridge.
The effectiveness of a combined delivery of medicaments may require one or more doses to be delivered sequentially with one of the two medicaments being injected into the human body prior to the delivery of the other medicament. Such treatment may be conducted with devices that include two separate dispensing mechanisms that are actuated independently from each other such that the dispensing mechanisms are activated successively. Sometimes patients require merely a dose of one of the medicaments, e.g. the primary medicament. The correct use of the device, however, may be hazardous for patients that are physically or mentally impaired or otherwise disadvantaged.
From WO 2012/072554 A1, a drug delivery device is known that comprises a variable dose setting mechanism coupled to a drive gear that is coupled to a driven gear of a fixed dose setting mechanism. The driven gear is fixed axially and rotationally to a worm gear that interfaces with a sprung rack such that rotation of the worm gear forces the sprung rack upwards against a spring. The drive gear comprises vertical splines on an inner portion of the drive gear. The variable dose setting mechanism engages with the first gear via the engagement of drive features of a drive sleeve with the vertical splines the drive gear until a certain dose of a second medicament is set by the fixed dose mechanism. Then, the drive features on the drive sleeve disengage from the vertical splines and allow the variable dose setting mechanism to set larger doses without further rotation of the driven gear.
A similar mechanism is described in WO 2012/072533 A1, where the mechanical coupling between a fixed dose setting mechanism and a variable dose setting mechanism includes a drive sleeve that disengages from a drive gear after a fixed dose of a second medicament is set.
WO 2012/072541 A1 describes a drug delivery device with a variable and a fixed dose setting mechanism interlinked by a mechanical coupling. The mechanical coupling includes a lift cylinder, a lifting collar and an engagement pin. The variable dose setting mechanism is rotated and the lifting collar is in engagement with the lift cylinder via the engagement pin. The stroke length where the lifting collar is in engagement with the lift cylinder is sufficient to lift the cylinder which in turn sets the fixed dose setting mechanism and stores energy with a spring. When the lifting collar disengages from the engagement pin, it is allowed to continue on its path to set a larger dose of the variable dose medicament.